1. Field of the Invention
The present invention relates to a polishing tool and apparatus for polishing a workpiece to be polished, such as a semiconductor wafer, to a flat mirror finish. More particularly, the invention relates to polishing technology using a polishing tool containing thermoplastic resin therein, such as a fixed abrasive or a polishing pad.
2. Description of the Related Art
As semiconductor devices have become more highly integrated in recent years, circuit interconnections have become finer and dimensions of devices to be integrated have become smaller. From this point of view, it may be necessary to polish and planarize a surface of a semiconductor wafer to remove a film (layer) formed on the surface of the semiconductor wafer. In order to planarize a surface of a semiconductor wafer, a polishing apparatus for performing chemical mechanical polishing (CMP) has been used. This type of chemical mechanical polishing (CMP) apparatus comprises a polishing table having a polishing pad (polishing cloth) attached thereon, and a top ring for holding a workpiece to be polished, such as a semiconductor wafer. The workpiece is disposed between the polishing pad and the top ring, and pressed against the polishing pad under a certain pressure by the top ring while the polishing table and the top ring are rotated. In this state, the workpiece is polished to a flat mirror finish while a polishing liquid (slurry) is supplied onto the polishing pad.
In a chemical mechanical polishing process as described above, a workpiece is polished while a polishing liquid (slurry) containing a large amount of abrasive particles is supplied onto a relatively soft polishing pad. Therefore, a problem of pattern dependence arises. Pattern dependence means that gentle irregularities are formed on a surface of a semiconductor wafer after a polishing process due to irregularities on the surface of the semiconductor wafer that existed before the polishing process, thus making it difficult to planarize the surface of the semiconductor wafer to a completely flat surface. Specifically, a polishing rate is higher in an area where irregularities have small pitches (a density of irregularities is large) and is lower in an area where irregularities have large pitches (a density of irregularities is small). Existence of areas of the higher polishing rate and areas of the lower polishing rate causes gentle irregularities to be formed on the surface of the semiconductor wafer.
In recent years, it has also been a common practice to polish a semiconductor wafer with use of a fixed abrasive (grindstone). In such a process, a surface of a semiconductor wafer or the like is polished with a fixed abrasive which comprises abrasive particles fixed by a resin as a binder. Since a semiconductor wafer is thus polished mainly by abrasive particles released from a binder in a fixed abrasive, a polishing liquid (slurry) is not basically required to be supplied onto a surface of the fixed abrasive during polishing. With a process utilizing a fixed abrasive which essentially has a large hardness, it is possible to achieve a considerably higher level of planarity. On the other hand, with the process utilizing a fixed abrasive, scratches or defects tend to be produced on a surface of a semiconductor wafer being polished.